The present application relates to operating an internal combustion engine at or near stoichiometric conditions, and further relates to regenerating an aftertreatment system and other challenges related thereto. The engine may be a spark ignited or compression ignition engine. Aftertreatment systems are required to bring emissions into compliance for many engine applications, and many aftertreatment systems require accurate control of air-fuel ratios to properly function and to regenerate. Further, regeneration of some aftertreatment system components in the absence of excess oxygen can be challenging. Accordingly, there is a demand for further improvements in this area of technology.
In other examples, the present application relates to controlling an aftertreatment system having a particulate filter and a NOx conversion device that converts NOx under rich or stoichiometric conditions. Many particulate filters require excess oxygen to properly oxidize and remove trapped particulates. NOx conversion devices that are not designed for lean operation have limited NOx conversion when oxygen levels are significantly higher than stoichiometric oxygen levels. Accordingly, operational challenges are presented in an aftertreatment system including a particulate filter and a NOx conversion device that is not designed for lean operation.